This invention relates in general to systems for operating hydraulically actuated devices. In particular, this invention relates to an improved system for operating a hydraulically actuated device that is provided on a movable vehicle.
Trucks and other types of movable vehicles are often equipped with one or more hydraulically actuated devices for performing a variety of functions, such as snow plowing, earth moving, and the like. In vehicles that are so equipped, a source of pressurized fluid is typically provided on the vehicle to operate the hydraulically actuated device in a desired manner. The engine of the vehicle allows the vehicle to be moved as desired, while the source of pressurized fluid allows the hydraulically actuated device to be operated to perform the desired function. Ideally, the source of pressurized fluid allows the hydraulically actuated device to be operated independently of whether the vehicle is moving.
Known sources of pressurized fluid for vehicular-mounted hydraulically actuated devices have typically been provided having one of three general types of structures. In the first type of structure, the source of pressurized fluid is an electrically operated hydraulic pump that is electrically connected to the electrical system of the vehicle. Although such electrically operated hydraulic pumps are effective, they have been found to be relatively difficult to maintain and, in some situations, may require customization of the electrical system of the vehicle in order to safely allow the necessary amount of electrical power to operate the hydraulic pump to be drawn. In the second type of structure, the source of pressurized fluid is a mechanically operated clutch pump that is connected to the engine of the vehicle by means of an aftermarket serpentine belt. Although such mechanically operated clutch pumps are also effective, they have been found to be relatively difficult to maintain, involve the use of customized installation hardware, and can place an unduly large load on the engine of the vehicle.
In the third type of structure, the source of pressurized fluid is a mechanically operated hydraulic pump that is driven by a power take-off unit connected to the transmission of the vehicle. Such mechanically operated power take-off unit/hydraulic pump assemblies avoid many of the drawbacks mentioned above. However, it is increasing common for trucks and other relatively heavy duty vehicles to be provided with automatic transmissions. The use of these power take-off unit/hydraulic pump assemblies in vehicles having automatic transmissions is often undesirable because the amount of power that is available for use from the power take-off unit is limited or non-existent when the automatic transmission is in a moving gear ratio (i.e., forward or reverse), but the vehicle itself is stationary. Thus, it would be desirable to provide an improved system for operating a hydraulically actuated device that is provided on a vehicle that avoids this problem.